Generally, a swash plate-type compressor suitable for an air-conditioning system for a vehicle is used such that a gaseous refrigerant, which is discharged at a low pressure from an evaporator, is compressed at a high pressure so as to be readily liquefied, and is then fed into a condenser.
The inside of the swash plate-type compressor is provided with a piston that compresses the refrigerant in the compression chamber of the compressor while performing reciprocal movement due to the rotation of the swash plate.
The swash plate, which rotates in a state of being inclined relative to the drive shaft, is configured such that the sliding surface thereof is in contact with the shoe of the piston, and thus the piston is reciprocally moved in the bore of a cylinder when the swash plate is rotated.
Therefore, the swash plate has to possess lubricating properties on the sliding surface that is in contact with the shoe, as well as mechanical properties including wear resistance.
Materials for the swash plate are largely classified into hypereutectic aluminum alloys, copper alloys, and cast iron.
The hypereutectic aluminum-silicon alloy for use in a fixed air-conditioning compressor is manufactured in a manner in which silicon particles are fined at a high cooling rate in the continuous casting process, and then forged. In order to increase the surface lubricating properties, a self-lubricating tin (Sn) coating process is applied.
For reference, the self-lubricating coating process is a coating technique using a material that reduces friction resistance even without the use of a friction material.
However, the hypereutectic aluminum-silicon alloy is expensive compared to typical aluminum products because continuous casting and forging is carried out, rather than typical gravity casting or sand casting due to the difficulty in controlling the size of silicon particles. Also, the seizure stress of the hypereutectic aluminum-silicon alloy is less than half that of the copper alloy or cast iron, making it difficult to apply the hypereutectic aluminum-silicon alloy to variable air-conditioning compressors which are subjected to high surface pressure and severe driving conditions.
In addition, the copper alloy and cast iron may be used as material for the swash plate for use in a variable air-conditioning compressor.
These two materials have superior mechanical properties, wear resistance, and seizure stress, and are thus currently applied to almost all variable air-conditioning compressors.
However, the copper alloy is expensive compared to conventional cast iron material or aluminum forged material, and the cast iron material suffers from the same seizure problems when driven because the sliding surface is made of the same material as in the shoe that comes into contact therewith, and a special resin coating must be essentially provided at the interface therebetween.
In consideration thereof, there is a need to develop a swash plate using a novel aluminum alloy, which is inexpensive and enables greater processing freedom compared to conventional hypereutectic aluminum-silicon alloys but exhibits wear resistance and seizure stress equal to or superior to those of copper alloys or cast iron materials.
The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art.